A 34-year-old man is hospitalized due to trauma sustained during a motor vehicle collision. He subsequently develops worsening shortness of breath and confusion and dies despite appropriate management. Autopsy examination shows scattered petechiae on the anterior thorax. Microscopic evaluation of his pulmonary vessels reveals the findings shown below.
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Which of the following most likely predisposed this patient to developing the observed histopathologic abnormality?
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The histologic section of this patient's lung shows an aggregate of fat globules, hematopoietic cells, and organizing thrombus lodged inside the pulmonary vasculature. This is consistent with bone marrow embolism, which occurs in fat embolism syndrome (FES).
FES classically presents with the triad of respiratory distress, neurologic impairment, and petechial rash within 24-72 hours following a long-bone or pelvic fracture. Severe skeletal injuries can cause fat globules to be dislodged from bone marrow into the bloodstream, where they form aggregates with platelets and red blood cells. These aggregates occlude pulmonary microvessels and impair gas exchange. Some fat emboli may be small enough to pass through the pulmonary circulation and cause microvascular occlusion in the systemic circulation, leading to the neurologic manifestations (eg, confusion) and petechial rash characterizing the condition. Release of toxic inflammatory mediators (eg, cytokines, free fatty acids) may also contribute to the neurologic manifestations and rash. Thrombocytopenia can occur due to platelet adherence and aggregation to circulating fat globules.
(Choice A) Aspiration of gastric contents can lead to aspiration pneumonitis or aspiration pneumonia. The lung parenchyma would demonstrate polymorphonuclear leukocyte infiltration and multinucleated foreign body giant cells.
(Choice B) Left ventricular dysfunction can lead to heart failure and pulmonary edema. Over time, alveolar fibrosis develops and there is accumulation of hemosiderin-laden macrophages, also known as heart failure cells.
(Choice D) Severe systemic infection, or sepsis, can lead to acute respiratory distress syndrome, in which parenchymal inflammation leads to accumulation of interstitial fluid and fluid leakage in the alveoli. Histopathology often shows diffuse alveolar damage.
(Choice E) Thrombosis in the deep veins can lead to acute pulmonary embolism. Due to localized ischemia, the adjacent lung parenchyma can demonstrate coagulative necrosis and hemorrhage.
Educational objective:
Fat embolism syndrome most commonly results from the release of fat globules from bone marrow following a long-bone or pelvic fracture. The fat globules form inflammatory aggregates that cause microvessel obstruction and systemic inflammation leading to the triad of respiratory distress, neurologic dysfunction, and petechial rash.